Spin-spin interaction in the 3T2g excited state of C60

The zero-field splitting found in spin resonance in the excited 3T2g state of neutral C60 has a lower symmetry than is predicted by the usual Jahn-Teller (JT) coupling theory. The effect of spin-spin coupling in the JT split state is discussed, and it is shown that the observed value of vertical stroke E/D vertical stroke, the ratio of the spin Hamiltonian constants, gives information about the nature of the distortion. It is proposed that the ground-state distortion departs slightly from D5d symmetry because of the presence of an unexpected, but small, high-order term in the energy. (orig.)